“Limbs have been amputated – people have lost feet and shins,” she said.

Some of the critically injured were being transferred to hospitals as far away as Moscow.

The authorities in Crimea have declared three days of mourning. A prayer service was held for the victims at a makeshift shrine near the college.

Image copyrightGetty ImagesImage caption Prayers were said for the victims near the college in Kerch

The rampage is the deadliest attack to have taken place in Crimea since the Russian annexation.

That Russian intervention – condemned by many Western powers – marked the start of a conflict pitting Russian-backed rebels in eastern Ukraine against Ukrainian government forces.

What happened at the college?

The perpetrator is said to have run from room to room as he fired. Minutes earlier he had left a rucksack containing the nail-bomb in the cafeteria on the ground floor and detonated it remotely, Russian Channel One TV reported.

Photos later emerged in Russian media purportedly showing his body in the college library.

The TV report described a scene of devastation and mass panic after the blast. It said doors and windows were shattered in the entrance hall and on the first floor, above the cafeteria. Some students leapt out of the building from a height of 5m (16ft 5in).

Investigators later said they had found a second explosive device among the gunman’s possessions and that it had been disarmed. He was also reported to have several packs of bullets and home-made petrol bombs.

BBC Russian spoke to witnesses, including Igor Zakharevsky. “I was at the epicentre of the first explosion, at the entrance, near the buffet,” he said.

“I was in complete shock and one of my classmates started pulling me away. Then I heard several shots at intervals of two or three seconds. After a while there was another explosion.”

Marina, an 18-year-old student at the college, said there was “a massive explosion, the windows began to rattle and everyone started screaming”.

“We bolted out of the classroom and ran. There was complete pandemonium in the corridor,” she said. “I saw a girl lying near the wall in an unnatural position, others lying on the floor covered in blood. Shots were being fired every five or six seconds.